427 
Krom the above table it is seen that in these properties also there 
are distinct indications of ' periodicity. The transitiorial elements 
Fe and Ni have practically equal values tbr these properties. 
As the atomie weight of elements in the sarne periodie group 
increases the value for Young’s modulus and torsional rigidity decreases. 
In the sub group B of the first group of periodie classification (Cu, 
Ag, Au), gold having the highest atomie weight lias the smallest 
values for Yoüng’s modulus and torsional rigidity. Similar are the 
behaviours of zinc, cadmium, tin and lead. 
Sufficiënt data are available in the case of the temperature coëfficiënt 
of torsional rigidity and hence distinct periodie curves are obtained ; 
the alkali metals, Li, K, Na, Rb and Cs lie on the topmost points 
whilst copper, silver and gold lie on a straight line on the minima. 
Specijic heat. During recent years the determination of specific 
heats of substances at low temperatures was attracting the attention 
of numerous investigators. 
Richards and Jackson (Zeit. Pliys. Chern, 1910. 70, 414) have 
carefiilly determined the specific heats of various elements between 
— 188° and -(- 20°. From their experimental data, they come to 
the conclusion that the atomie heats of various elements between 
the above range of temperature conform approximately to Dulong 
and Prtit’s law, the value of the constant being 5.3. There are 
28 
Verslagen der Afdeeling Natuurk. Dl. XXIV. A°. 1915/16. 
